Differentially cured materials and process for forming same

ABSTRACT

A structure includes a layer which includes a first cured portion and a second cured portion which are formed from a same light curable material. The first cured portion is cured to a first amount, and the second cured portion is cured to a second amount. The first amount is sufficiently different than the second amount to result in a visible discontinuity on the surface of the structure. A method for forming a pattern in a radiation curable material includes providing between a radiation source and the radiation curable material, a pattern that can block a portion of the radiation from the radiation source. The material is cured with radiation from the radiation source to form a pattern in the radiation curable material.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/928,247 filed Aug. 10, 2001, which claims the benefit of U.S.Provisional Application No. 60/226,697, filed on Aug. 18, 2000, and U.S.Provisional Application No. 60/256,176, filed on Dec. 15, 2000.

The entire teachings of the above applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

Many retroreflective sheeting, collimating films, etc. are made toexacting dimensions in metal molds that are difficult and expensive tomake. The metal molds can represent a significant barrier of entry intoa high quality market for sheeting and films. However, knock-offmanufacturers of retroreflective sheeting and collimating film can forminexpensive, low quality molds from the high quality sheeting and film.As a means to deter such copying, the metal molds are often engravedwith a company logo or trademark, which can cause the logo or trademarkto appear on the knock-off end product. A disadvantage of the added logois that it can be more difficult to engrave at the tolerances required.

Therefore, a need exists for better marked products and a method ofmarking products better.

SUMMARY OF THE INVENTION

A structure includes a layer which includes a first cured portion and asecond cured portion which are formed from a same light curablematerial. The first cured portion is cured to a first amount, and thesecond cured portion is cured to a second amount. The first amount issufficiently different than the second amount to result in a visiblediscontinuity on the surface of the structure. The layer can beconnected to a base. The layer and the base can be formed of the samematerial. The first amount of curing can be sufficiently different thanthe second amount of curing to result a difference in the thickness ofthe first portion and the thickness of the second portion that is in arange of between about 0.05 and 2.0 micrometers. A visible discontinuityis considered a rise or depression in the surface of a structure thatcauses incident light to display a different shade of light that whenincident light strikes a portion of the surface not having a rise ordepression. The visible discontinuity can be discerned with the nakedeye. The layer can be a prism array, such as linear prisms orcube-corner prisms, a lenticular structure, or a sub-wavelengthstructure.

A method for forming a pattern in a radiation curable material includesproviding between a radiation source and the radiation curable materiala blocking pattern that can block a portion of the radiation from theradiation source. The material is cured with radiation from theradiation source through the blocking pattern to form a pattern in theradiation curable material.

A pattern transfer structure includes a radiation source for emittingradiation, a radiation curable material that can be cured by theradiation and a pattern for blocking a portion of the radiation. Thepattern is disposed between the radiation source and the radiationcurable material during the curing of the material such that a patternis formed in the material.

A method for forming a prism structure includes providing a prism moldand placing a radiation curable material in the mold. A pattern isprovided between a radiation source and the radiation curable materialthat can block a portion of the radiation curable material. Theradiation curable material is cured with radiation from the radiationsource to form a pattern in the radiation curable material.

A prism structure includes a base and a prism array connected to thebase. The prism array includes a first cured portion and a second curedportion which are formed from a same radiation curable material. Thefirst cured portion has a first index of refraction value and the secondcured portion has a second index of refraction value which issufficiently different from the first index of refraction value toresult in a visible discontinuity on the surface of the structure.

The invention has many advantages including forming a permanent patternin materials that are transparent and do not significantly detract fromother functions. The material can have the pattern act similar to awatermark in paper to provide a means of identification for a product'ssource that is difficult to forge. Also the pattern can serve as afunction of light management by altering the path of light that istransmitted through such a structure having the pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an isometric view of a radiation curable material and apattern layer positioned thereover for forming a pattern in the curablematerial.

FIG. 2 shows an isometric view of the radiation curable material havinga pattern formed therein.

FIG. 3 shows an isometric view of a retroreflective structure havingmoth-eye structures formed thereon, the moth-eye structures having apattern formed therein in accordance with another embodiment of theinvention.

FIG. 4 shows a perspective view of a standard collimating film.

FIG. 5 shows a perspective view of a differentially cured collimatingfilm.

FIG. 6 shows a schematic view of a method for forming the differentiallycured collimating film.

FIG. 7 shows a cross-sectional view of another embodiment.

FIG. 8 shows a perspective view of the embodiment in FIG. 7.

FIG. 9 shows an embodiment of a logo pattern.

FIG. 10 shows a plot of a surface profile with an interferencemicroscope trace which was made across the surface of a film made withthe pattern transfer process.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. All parts and percentages are by weightunless otherwise specified.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows.Generally, the invention is directed to forming a pattern in a radiationcurable material. The pattern, in one embodiment, is transparent whenviewed in a direction substantially normal to the material. However, thepattern can be seen more clearly at a viewing angle of about fifteendegrees from the normal.

FIG. 1 illustrates an embodiment of the present invention for forming apattern, such as exemplary pattern “ABC” provided by, for example, maskor pattern layer 10, disposed between a radiation source 14 and aradiation curable material 12. In one embodiment, the mask layer 10 caninclude polycarbonate, polyethylene, polybutylene or the like, and mayinclude a low-tack adhesive. The curable material 12 can includecoatings and microstructured or patterned materials formulated frommaterials, such as polyester, urethane, or epoxy acrylates andmethacrylates. Various additives including fillers, free-radicalinitiators and cationic initiators can be included in the material 12 toimprove processing or performance. See, for example, Sartomer CompanyBulletin Nos. 4018 or 4303, the teachings of which are incorporated byreference. The radiation source 14 preferably provides actinicradiation, which causes photochemical activity in the curable material12. For example, typical ultraviolet light can be used.

The pattern layer 10 can include any kind of material that blocks atleast a portion of the radiation from the radiation source to leave asimilar pattern in the cured material 12. For example, the pattern canbe formed by a colored pattern, such as, using common printing inks,printed on a transparent polymer film. The pattern can also be formed byembossing patterns that effect the transparency of the film. In oneembodiment, the pattern can be applied directly on either side of asubstrate which carries the curable material 12 and after curing, thepattern may or may not be removed to leave the cured pattern in thecured layer 12. In alternative embodiments, the pattern layer 10 caninclude a stencil or the like, such as a colored or semi-transparentfilm material or a clear resin with ultraviolet blocking chemicaltherein.

As shown in FIG. 2, the pattern layer 10 has been removed but thepattern “ABC” has been transferred to the cured material 12. It isbelieved that the pattern changes the curing rate of the material 12 toform the pattern in the cured material. One theory suggests that themolecules in the formed pattern are denser as the molecules have alonger time to cross-link than the molecules which do not have a maskthereover. These denser regions appear to have different indices ofrefraction. The pattern is best viewed at an angle of about fifteendegrees.

FIG. 3 illustrates another embodiment for forming a pattern in amaterial. In this embodiment, a pattern layer 10 is positioned over acured retroreflective structure 16 which can contain, for example,linear or cube-corner prisms. Examples of suitable cube-corner prismsare disclosed in U.S. Pat. No. 3,684,348, issued to Rowland on Aug. 15,1972, the teachings of which are incorporated herein by reference.

Moth-eye structures 18 can be formed on the opposite side of theretroreflective structure 16 as shown in FIG. 3. Moth-eye structures areexplained in more detail in U.S. application Ser. No. 09/438,912, filedon Nov. 12, 1999, which corresponds to International Publication No. WO01/35128, published on May 17, 2001. The teachings of each areincorporated herein in their entirety. The moth-eye structures 18 arecured by the radiation source 14 through the pattern layer 10 such thatthe pattern is formed in the moth-eye structures 18 or diffusingstructure or other suitable structures.

A sub-wavelength structure applied preferably has an amplitude of about0.4 microns and a period of less than about 0.3 microns. The structureis sinusoidal in appearance and can provide a deep green to deep bluecolor when viewed at grazing angles of incidence. Preferably, theamplitude is greater than two times the period to provide a two orgreater to one aspect ratio.

To form a sub-wavelength structure, the structure is first produced on aphoto resist-covered glass substrate by a holographic exposure using anultraviolet laser. A suitable device is available from HolographicLithography Systems of Bedford, Mass. An example of a method isdisclosed in U.S. Pat. No. 4,013,465, issued to Clapham et al. on Mar.22, 1977, the teachings of which are incorporated herein by reference.This method is sensitive to any changes in the environment, such astemperature and dust, and care must taken. The structure is thentransferred to a nickel shim by an electroforming process.

In another embodiment, a fine pattern can be formed on the mask layer10. For example, the pattern can be a few tenths of a millimeter or lessin width. A curable material, which is preferably substantially clearwhen cured, is formed on the opposite side of the mask layer 10 of thepattern and cured by a radiation source 14. The fine pattern is thustransferred to the cured material. The mask layer 10 is removed and thecured sheet is placed in front of a display, such as a liquid crystaldisplay. The fine pattern breaks up the pixel pattern in the displaywithout as much light loss as with diffuser sheets.

In radiation cured casting processes where it is desirable to producefeatures with multiple angles, one normally cuts multiple angle featuresinto the mold that is used for the reproduction of the features: This iscommonly true in the manufacture of light guiding or light reflectingproducts where small angle changes can strongly affect the productperformance. The cutting and replication of molds are costly and timeconsuming processes.

With this invention, one can produce a variety of angle and patternvariations in a product from a single mold design. One prints a“photomask” onto the surface of a carrier sheet or film prior toformation and radiation cure of a mold formed structure. The “photomask”can be clear or colored and be applied to either side of the carrier. Ifthe curing radiation is highly collimated, it is desirable to have the“mask” be semi-transparent to allow for slow curing in that area. Incases where the radiation is less collimated, one can obtain curethrough totally opaque masks via scattering and reflections into themasked area.

The resulting product then displays different optical behavior in areasthat have been masked due to the variation in shrinkage and refractiveindex related to the speed of cure which is hindered by the “mask”.

FIG. 4 shows a perspective view of a typical collimating film 30 withlinear prisms 32 having linear peaks 34 and valleys 36. The dihedralangle of the first side 36 and second side 38 of the peak 34 istypically ninety degrees. However, it can be a non-right angle. Thelinear prisms 32 can be formed on a base film 40.

FIG. 5 shows a perspective view of a prism array 52 of a differentiallycured collimating film 50. Many of the prisms which are not blocked by amask, such as prism 54, have a linear peak 56. Many of the prisms, whichare blocked, such as prism 58, have a curved peak 60. The curved peak isthe result of curing through a mask which reduces or increases the curerate with respect to the surrounding areas. Typically, curved peak 60 isshaped compared to the normal apex of linear peak 56 of prism 58. Theregion 62 is curved in respect to another region which can result in awider light distribution. The curved center line 66 of the peak in thisprism can be off center in respect to the normal center line 64depending upon the curing mask used. This region 62 also can have aslightly different index of refraction in respect to other areas. Theprisms can be formed on a base film 68, such as a polyester,polycarbonate, polyurethane, acrylic and polyvinyl chloride. Preferably,the mask can cover up to about fifty percent of the area of the productto be formed, such as a collimating film. The shape of the differentialcure area can be essentially any configuration or size. This allows oneto tailor the light/distribution in specification areas of the sheet,such as to corners or edges, instead of the center of the sheet. Also,if a greater percentage of the area of the structure were blocked ascompared to exposed to ultraviolet light, the exposed portion can resultin raised portions or bumps. In structures where a lesser percentage ofthe area of the structure were blocked as compared to exposed toultraviolet light, the structure can have an appearance with recesses.

In the area which was blocked, the prisms can have nanometer sizestriations caused by the differential cure shrinkage pattern. Thesestriations can perform like a vertical linear moth-eye structure. Somestriations can extend from the peak to valley. The striation can rangein width of between about 250 and 770 nanometers depending on the maskpattern. The striations can cause upward light tunneling.

Many other types of prisms can be used including cube-corner prisms.Cube-corner or prismatic retroreflectors are described in U.S. Pat. No.3,712,706, issued to Stamm on Jan. 23, 1973, the teachings of which areincorporated by reference herein. Generally, the prisms are made byforming a master negative die on a flat surface of a metal plate orother suitable material. To form the cube-comers, three series ofparallel equidistance intersecting V-shaped grooves sixty degrees apartare inscribed in the flat plate. The die is then used to process thedesired cube-corner array into a rigid flat plastic surface. Furtherdetails concerning the structures and operation of cube-cornermicroprisms can be found in U.S. Pat. No. 3,684,348, issued to Rowlandon Aug. 15, 1972, the teachings of which are incorporated by referenceherein. Also, the pattern transfer concept can include forming astructured coating onto a smooth surface and also forming a patternstructure onto a micro optical array of any type including submicron tomicron size surfaces. Further, a pattern can be placed on planosurfaces, prism surfaces, lens structures, and others. The pattern canbe random, ordered or designed to convey a message.

Referring now to FIG. 6, a method for forming the differentially curedcollimating film will now be described in further detail. A mold 102 isruled with linear grooves 104 essentially parallel to the axis aboutwhich the mold rotates. The linear grooves can be pitched between about0.05 and 0.2 mm (0.002 and 0.008 inches). A base film 104 is unrolledfrom roll 106. The base film 104 can be a suitable material, such as apolyester. Mask film 108 is unrolled from second roll 110. Mask film canbe formed of a suitable material, such as polyester, upon which anon-transparent design is printed on the transparent mask film. Thenon-transparent design can be printed on the mask film in the samemanner as a design is printed on an overhead transparency. The base film104 and mask film 108 are pinched together by first pinch roller 112against roller 102. The base film 104 and mask film are kept in closecontact with mold 102 until second pinch roller 114. In anotherembodiment, base film and mask film can be laminated together as asingle sheet and then unrolled from a single roll.

In yet another embodiment, a removable pattern can be directly printedon a first side of the base film with a suitable light blockingmaterial, such as a water soluble ink or the like. A curable layer oflight curable material is placed on the second side of the base film,and the curable layer is differentially cured in the presence of lightdirected through the pattern and base film to the curable layer. Afterdifferentially curing the layer, the removable pattern is removed fromthe base film. For example, it can be removed with a solvent, such aswater for a water soluble ink. However, other solvents can be used, suchas alcohol, hydrocarbons, etc., depending upon the ink or other materialused to form the light blocking pattern on the base film. An advantageof this embodiment is that a separate mask film is not needed.

Prism monomer material 116 is placed at point 118 proximate to pinchroller 112. The monomer material, such as an acrylic, flows into thegrooves 120 of mold 102. The prism monomer material 116 is cureddifferentially by the partially blocked ultraviolet light as it passesultraviolet lamps 122, 124, to form differentially cured collimatingfilm 126. Differentially cured collimating film 126 is wound up on windup roller 128. The mask film 108 is wound up on second wind up roller130.

In a collimating film having portions that are differentially cured,light is directed through the collimating film that results in differentshades of lighting. Lighter portions include the regions with ninetydegree linear prisms. Regions with darker portions include the prismsthat were differentially cured by blocking by the mask. In these darkerportions, the prisms are slightly distorted due to the different curerate and appear darker because the light is spread over a broader range.

A light directing film sheeting can be used for collimating light inbacklighting systems. The light directing film sheeting 200, as shown ina cross-sectional side view in FIG. 7 and in a perspective view in FIG.8, includes a base film 202 formed of a transparent polyester film, suchas ICI Dupont 4000 PET, or polycarbonate, such as Rowland Technologies“Rowtec” film, having a thickness in the range of between about 50 and250 micrometers (0.002 and 0.01 inches). In a preferred embodiment, thesheeting can have a thickness in the range of between about 0.1 and 0.15mm and (0.004 and 0.006 inches) and an index of refraction in the rangeof between about 1.49 and 1.59.

A series of transparent linear prisms 204 having sides 206 are formedover the base film 202. Sides 206 can be isosceles. The linear prisms204 extend across the sheeting. The prisms are formed of a transparentresin, such as a mixture of polymerized CN104 polyacrylate availablefrom Sartomer Chemical Co. and RDX51027 from UCB Chemical. The linearprisms are pitched a distance (p) in a range of between about 25 and 100micrometers (0.001 and 0.004 inches), preferably about 48 micrometers(0.0019 inches) per prism. The linear prisms have a height (h) in arange of between about, 20 and 100 micrometers (0.0008 and 0.004 inches)preferably about 25 micrometers (0.001 inches). The linear prisms havepointed peaks 206 with a peak angle (ÿ) as desired, with preferredvalues of 88 or 90 degrees in a sheeting. Base angles ÿ₁ and ÿ₂ can bethe same or different. The linear prisms 204 can be attached to the basefilm 202 by an optional prism adhesive layer 208, such as 7650TC acrylicadhesive available from Bostik Chemical. Prism adhesive layer 208 has athickness (a₁) in the range of between about 2.5 and 12 micrometers(0.0001 and 0.0005 inches).

On the non-prism side 210 of the base film 202, a pattern structure 212is formed, such as with a resin composition similar to or the same asthe prism side adhesive layer. The pattern structure 212 can be attachedto the base film 202 by pattern adhesive layer 214, which is similar inmaterial and thickness (a₂) to prism adhesive layer 208. Patternstructure 212 has a thickness in the range of between about 2.5 and 12micrometers (0.0001 and 0.0005 inches).

As shown in FIG. 9, the pattern structure 230 includes a logo 232, whichis an arrangement of four obtuse scalene triangles. The logo can be acompany name, a trademark, a figure, or other desired design. Thepattern structure can be printed on sheeting such as a polyesteroverhead projector sheeting by a laser printer. In the shown embodiment,the logo is repeated in a line on a first axis about every 13 mm. Thelogos in each line are off-set in the next by a half of a logo and thelines repeat about every 7.5 mm along a second axis in the run/webdirection, which is perpendicular to the first axis. The lines of thelogo are about 0.5 mm in width. Other types of designs include crosshatching, geometric figures, numerals, letters, etc.

Returning to FIG. 8, the lines are depressions 216 or recesses in thesurface of the non-prism side. Depressions 216 can have a depth (d) inthe range of between about 0.3 and 2.0 micrometers with an average depthof one micrometer. The depressions are not uniform in slope from edges218 to low point 220. The depressions can have an average slope of 0.5degrees to the surface of the base film 102 with the slope being as highas one degree.

The pattern structure is formed by placing a mask film temporarily onone side of the base film. The mask film has a logo, geometric form(lines, circles, curves, etc.), alphanumerics or any other desireddesign formed thereon that can block a portion of the ultraviolet lightas it passes from ultraviolet light source through the mask film to thebase film. The portion of the mask film without the logo printed thereonis more transparent to ultraviolet light. On the other side of the basefilm, an adhesive layer is deposited and an uncured radiation curableresin is placed on the adhesive layer. Ultraviolet light is directedfrom an ultraviolet light source through the mask layer through the baselayer through the adhesive layer to the resin layer. The resin layer isdifferentially cured because the ultraviolet light intensity is blockedunevenly by the printed patterned to the resin layer resulting in thepattern structure. The pattern structure is uneven and segmented. Theportions of the resin layer that have the greatest blockage from theultraviolet light have the deepest depressions into the surface. Theportions that were exposed to ultraviolet light resulted in segmentswith relatively flat surfaces. The mask film is then removed from thebase film. The linear prisms are cast on the same side of the base filmwhere the mask film had been placed. The linear prisms are cured byultraviolet light directed through the base film. The linear prisms canbe slightly differently cured in the portions that are exposed to theultraviolet light that passes through the pattern structure that isuneven and segmented.

The film can be placed between a light guide and a display, such as aliquid crystal display. The fine pattern breaks-up the pixel pattern inthe display without as much light loss as with a diffuser sheet. Thepattern structure on the film can be readily visible across the film.

The film can be used as a single sheet or as a two-sheet or more system.A two-sheet system has the linear prisms peaks pointed in the samedirection and the length of the peaks on each sheet are often crossed atninety degrees.

EXAMPLE 1

Linear prisms were cast on polycarbonate and covered with a number 30LCmask film (manufactured by Ivex Packaging Corporation) that had a bluecolored “PEEL” pattern printed on it. Moth-eye structures were cast onthe opposite side of the prisms and cured by ultraviolet radiation at aweb speed of about twelve meters per minute (forty feet per minute) pasttwo 157-236 watts/lineal centimeter (400-600 Watts/lineal inch)ultraviolet lamps manufactured by Eye Ultraviolet Corporation. Afterremoving the mask film, the cured moth-eye structures retained the“PEEL” pattern which could not be readily seen at a zero degree viewingangle but were pronounced at about a fifteen degree viewing angle.

EXAMPLE 2

Alphanumeric images were handwritten onto the surface of a mask film ona cling mask sample of polycarbonate film manufactured by RowlandTechnologies Incorporated. Commonly available felt tip marker pens wereused to form the images. An ultraviolet curable coating of epoxyacrylate was applied to the other side of the polycarbonate film andcured under a 236 Watts per lineal centimeter (600 Watts per lineal)inch lamp at about 4.6 meters per minute (fifteen feet per minute). Themask film was removed and the cured coating was visually examined atvarious angles. The images that had been on the mask film were visibleat shallow viewing angles in the cured coating.

EXAMPLE 3

FIG. 10 shows a plot of a surface profile with an interferencemicroscope trace which was made across the surface of a film made withthe pattern transfer process.

The height of the features is slightly less than one wavelength of redlight. Red light wavelength is 632.8 nm (2.49×10⁻⁵ inches). The heightof the features is approximately 500 to 900 nm (1.9685×10⁻⁵ to3.5433×10⁻⁵ inches). The average height is about 640 nm (2.5197×10⁻⁵inches).

The height and slope of the features caused some light deviation as thelight passes through the film. However, the effect on brightness appearsto be positive by about a one percent gain. Additionally, these featurescan act as resting points for the prism peaks of collimating films asthe films are stacked upon each other and therefore prevent the majorityof the prism peaks from being damaged by abrasion.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. An apparatus for forming an optical film comprising: a mold fordefining a shape for optical structures in the optical film; a liquidmaterial dispenser, wherein said liquid material dispenser feeds aradiation curable liquid material to the mold; a continuous mask film,for defining a pattern that further defines areas of the optical filmwhere curved portions are to be made in the optical structures therein;a continuous base film dispenser, for feeding a transparent base filmbetween the mask film and the mold; and a radiation source positionedfor simultaneously curing and patterning the liquid material byirradiating the liquid material through the overlapping mask film andbase film, such that the liquid material is cured to form the opticalfilm, and such that the curved portions as defined by the mask film arepatterned in the optical structures at the same time that they arecured, via differential exposure to the radiation in an area of theradiation curable liquid material blocked from the radiation source bythe pattern.
 2. The apparatus of claim 1 wherein the optical structuresare formed in a surface of the optical film that is opposite a surfaceof the optical film that contacts the base film.
 3. The apparatus ofclaim 1 wherein said radiation source emits ultraviolet light.
 4. Theapparatus of claim 1 wherein said radiation curable monomer material isselected from a material consisting of polyester, urethane, epoxyacrylates or methacrylates.
 5. The apparatus of claim 1 wherein thepattern is configured in the form of a logo, geometric forms oralphanumerics.
 6. The apparatus of claim 1 wherein a first cured portionhas an index of refraction that is different than the index ofrefraction of a second cured portion.
 7. The apparatus of claim 1wherein a first cured portion has a density that is different than thedensity of a second cured portion.
 8. An apparatus for making acontinuous optical film having parallel prism structures, the apparatuscomprising: a rotating cylinder mold having linear grooves formed on anouter surface thereof, the linear grooves used as a mold for definingthe parallel prism structures with aligned peaks; a liquid materialdispenser, wherein said liquid material dispenser feeds a radiationcurable liquid material onto the rotating cylinder mold at a dispensinglocation; a first roller, for supplying a continuous, radiationtransparent optical base film; a second roller, for supplying acontinuous mask film near the dispensing location, the continuous maskfilm having a pattern used in further defining features of the opticalbase film; a first pinch roller, for placing the continuous mask filmadjacent to the continuous optical base film near the dispensinglocation, and for positioning the optical base film and mask filmagainst the rotating mold such that the optical base film is positionednearest the rotating mold and the mask film is positioned outside of theoptical base film; a radiation source, disposed after the first pinchroller, for providing radiation for simultaneously curing and patterningthe liquid material by irradiating the liquid material through theadjacent mask film and optical base film, such that the radiationtravels first through the mask film and then through the transparentoptical base film before curing the liquid material, and such that theradiation source causes simultaneous patterning of the liquid material,to thereby define the optical base film and form deformations in theprism peaks in an area of the liquid material blocked from theirradiation by the pattern; a second pinch roller, disposed at a secondlocation adjacent the rotating mold, for further holding the mask filmand optical base film in position with respect to the rotating mold; afirst wind-up roller, for collecting the optical base film; and a secondwind-up roller, for collecting the mask film.